ANALYSIS OF PEPTIDES BY AMINO-ACIDS COMPOSITION - CONTRIBUTION OF ULTRAVIOLET DERIVATIVE SPECTROPHOTOMETRY AND RETENTION TIME PREDICTION

Amino acid composition analysis is sometimes used for the identificati on of peptides obtained from the hydrolysis of a protein of known sequ ence. Nevertheless, the interpretation of the analysis can be difficul t if only one hydrochloric acid hydrolysis can be performed because of the partial destruction of some amino acids and the lack of cleavage of certain peptidic bonds. In this paper we propose combining the anal ysis of amino acids by two techniques (derivative UV spectrometry and retention time estimation) associated on-line with the purification st ep of the peptides (reversed-phase HPLC). A set of 56 peptides from th e peptic and chymotryptic hydrolysis of bovine alpha(s1)-casein (alpha (s1)-CN) were analysed in this manner. The difference between the theo retical and observed retention times was 1.9 min, for aromatic amino a cids ratios the difference was 4.0%. The ambiguities coming from repea ted residues in the sequence or the presence of Trp residues, destroye d by acidic hydrolysis, were solved and a fragment of the alpha(s1)-CN sequence could be attributed to each peptide.